Many telecommunications switching systems might include plurality of I/O Cards (called line cards) for processing different data from network interfaces like E1, DS1, STM-n, OC-n etc and send this processed data to traffic switch (Called Switch card) to switch data from one network interface to other. In such telecommunication systems the data from Line cards to switch card passes over a backplane which connects various cards in a system. Such telecommunication system is called network element. In a network there is plurality of such network elements. In networks like SONET/SDH, all these network elements need to work in locked mode traceable to PRC (Primary reference clock). For more information on network synchronization in SDH refer ITU-T standard G.813 and G.825. The synchronization from one network element to other is passed over various interfaces like E1, DS1, STM-n, OC-n etc. Each network element extract synchronization clock from one of these predefined interfaces and synchronize the network element (system synchronizer) so that all the outgoing interface from the said network element are in sync.
Further, to avoid single point of failure, it is well know method in telecommunication systems to replicate critical sub systems like power supply, switch card, network element controller (Called chassis controller), system synchronizer etc. Such sub systems are called redundant sub systems, one acting as master and one or more acting as slave sub systems.
In such redundant “system synchronizer” sub systems, the line cards, switch cards needs to switch from master synchronizer to slave synchronizer when master sub system fails or user initiates a switch over. In systems where the traffic switch and system synchronizer sub systems are on separate cards, the switch and Line cards need to switch form master synchronizer to slave synchronizer at the same time to avoid ppm (parts per million) difference in the system clock used by traffic switch and Line cards. This is not easily implementable.
Further it is very common to integrate traffic switch and system synchronizer in a single card to achieve more number of network interfaces in a given network element and to reduce cost. Also it is very common to use slave traffic switch using the timing from the slave system synchronizer and master traffic switch using timing from master system synchronizer. In such systems the above said problem (ppm difference in the system clock used by line cards and traffic switch during system synchronizer switch over) is more severe which lead to temporary or permanent logic errors which in turn lead to traffic hit. To recover from permanent traffic errors, system needs to be restarted. For bigger systems this may lead to traffic down for few seconds. Thus, prior techniques often do not allow the system to continue operating, uninterrupted and maintaining substantial data integrity.
In light of the foregoing discussion, there is a need for a method and device to solve the above mentioned problems.